Following the progress in different technological fields, various kinds of compact electronic products with multiple functions have been developed. Digital still cameras, personal computer (PC) cameras, web cameras and mobile phones all are electronic products equipped with an optical pickup device or lens. Recently, even the personal digital assistants (PDAs) are equipped with an optical pickup device or lens in response to the consumers' demands. For these electronic products to be convenient for carrying and meet the requirement for humanization, the optical pickup device for these electronic products must not only provide good image quality, but also have relatively small volume and low manufacturing cost to enable increased applicability thereof. The above-mentioned requirements or conditions are particularly important when the optical pickup device is applied in mobile phones.
The conventional spherically polished glass lenses have been widely accepted by the field of optical devices because there is a wide choice of materials for them and they are advantageous in terms of chromatic aberration correction. However, when the spherically polished glass lenses are applied in cases that require a relatively small F number and a relatively large field angle, the problem of correction of spherical aberration and astigmatism still exists. To overcome the drawbacks in the above-mentioned conventional spherically polished glass lenses, there are optical pickup devices using aspheric plastic lenses or aspheric molded glass lenses to obtain better image quality. US Patent Publication No. 2007/0091457; U.S. Pat. No. 6,515,809; U.S. Pat. No. 7,262,925; US Patent Publication No. 2007/0195432; US Patent Publication No. 2005/0128334; and JP Patent Publication Nos. 2007-121820, 2005-352317, 2004-163786, 2007-094113, 2005-338234, 2007-047513, and 2006-098976 all disclose optical pickup lens structures including three pieces of lens elements. The differences between the above-mentioned patent disclosures or the technical features thereof are determined simply based on changes or combinations of the following factors: (1) the shapes of the three lens elements; for example, the first, second and third lens elements can all be meniscus-shaped, or the first and second lens elements are meniscus-shaped while the third lens element is planoconcave-shaped or planoconvex-shaped; and/or (2) the orientations of the convex/concave surfaces of the three lens elements; for example, the first, second and third lens elements may have their convex/concave surfaces arranged at the object side or the image side or in different combinations; and/or (3) the negative/positive refractive power of the three lens elements, such as in the case disclosed in JP Patent No. 3717488.
It can be known from the above-mentioned patent disclosures that the designs of the three-piece optical pickup lenses in the prior art are aimed at the forming of different changes in or combinations of lenses for the application in different optical purposes. Since these designs use lenses that have different shapes, combinations, functions or effects, they are considered as novel or inventive.
In recent years, optical pickup lenses to be applied in small-size cameras are required to have miniaturized size, short focal length, and good aberration adjustment ability. Among various miniaturized three-piece optical pickup lens designs, it is found a pickup lens including a first lens having positive refractive power, a second lens having negative refractive power, and an M-shaped third lens with an inflection point to enable gradually changing positive and negative refractive power is most ideal for achieving the requirement of miniaturization.
To enable different imaging manners, EP Patent No. 1830210; JP Patent Publication Nos. 2008-139853 and 2006-178328; U.S. Pat. Nos. 7,397,613; 7,486,328; 7,423,817; 7,468,847 and 7,515,358; US Patent Publication Nos. 2007/0195426; 2007/0217034; 2007/0229986 and 2008/0239510; TW Patent Publication No. 200639432; CN Patent Publication Nos. 1670560 and 1873460 disclose three-piece pickup lens including a first lens of positive refractive power, a second lens of negative refractive power and an M-shaped third lens of positive refractive power. On the other hand, EP Patent Nos. 1840618 and 1942363; U.S. Pat. Nos. 7,460,315; 7,460,314; 7,450,323 and 7,511,899; US Patent Publication Nos. 2007/0229987; 2008/0225401; 2008/0266679 and 2007/0195426; JP Patent No. 3816093; JP Patent Publication Nos. 2008-276200; 2008-233222 and 2007-010773; WIPO Patent WO2007039980; and CN Patent 1945372 disclose three-piece pickup lens including a first lens of positive refractive power, a second lens of negative refractive power, and an M-shaped third lens of negative refractive power.
In the application of optical pickup lenses, what are currently most needed by general users are the optical pickup lenses used with mini or low-profile devices, such as mobile phones, and the optical pickup lenses used with web cameras. These optical pickup lenses have a small lens diameter (i.e. a small effective lens radius), a short full lens length (i.e. a short overall lens length), a short distance between the image sensing device and the lens (i.e. a short back focal length), and good aberration correction. The means adopted by the prior art to solve these problems include the use of different lenses to constitute the optical pickup lens, the use of different lens shapes, or the use of different related optical parameters. However, to achieve the object of further miniaturizing (slimming) the optical pickup lens while simplifying the design and the manufacture thereof, the inventor of the present invention proposes an optical pickup lens that includes a second and a third lens both being an M-shaped lens, in order to effectively shorten the back focal length and widen the field of view of the optical pickup lens, allowing the same to be applied to mini and slim mobile phones or other optical systems.